An aircraft includes a very large number of pieces of electrical equipment or apparatus of various kinds. They may be motors or indeed electronic devices such as computers.
Among such pieces of equipment, many are electrically powered with a single phase. For this purpose, the equipment is connected to the positive terminal of the generator by means of a cable. As for the connection to the negative terminal generator, this takes place by connecting the other terminal of the equipment to the metal ground of the airplane which also has a negative terminal of the generator connected thereto. That constitutes the circuit for operating currents.
It is also necessary to make provision for carrying possible fault currents relating to the equipment. By way of example, this type of current may be a leakage current or a short circuit current and it may appear in the event of an anomaly. When the airplane is made mostly out of metal, fault currents can be carried in the same way as operating currents, with the equipment being connected to metal parts of the airplane.
However things are different when it is desired to make a portion of the airplane out of composite material comprising a plastics material matrix reinforced by non-metallic fibers. Such a material is a less good conductor of electricity than is metal.
In order to connect the metal ground of the aircraft to the pieces of equipment present in an aircraft of this type so as to carry operating currents, each piece of equipment is connected to said ground by means of a specific cable. It is thus known to envisage a specific metal network that, in the fuselage, is sometimes referred to as being the electrical structure network or “ESN”.
Furthermore, provision must be made for a possible fault current from the equipment to return to metal ground. For this purpose, a specific fault network is used that is referred to as the metallic bonding network or “MBN”. This network coincides in part with structural metal parts of the airplane such as seat rails in order to provide the airplane with a mesh or lattice capable of carrying fault currents from equipment. In this context, it is known to provide specific components such as metal tapes on each frame and each crossmember of the airplane so as to provide electrical continuity between the metal parts of the airplane in spite of the presence of the composite material, which continuity serves to carry fault currents to the ground of the airplane.
However, together these metal elements can form a mesh that is complex and that gives rise to numerous problems. Thus, adding specific components increases the weight of the airplane. It increases the length of time needed for accomplishing all assembly operations. The associated cost is not negligible. These elements also make the current return network more complex. Such elements require special studies to be made relating to dimensioning, to maintenance, to corrosion, and to interconnecting different portions of the ESN.